1. Field of the Invention
The present invention relates to an electronic device of an element row type such as a thermal head or an image sensor comprising a plurality of elements which are arranged in one row and are divided into a plurality of blocks to be sequentially driven in a block-by-block manner and, more specifically, to an improvement in such a device so as to reduce the area of the lead wiring electrode pattern and to realize the miniaturization of the device.
2. Description of the Prior art
Generally, such an electronic device as a thermal head, an image sensor, an LED display, a liquid crystal device or a print stylus device usually employs a divided-block driving system, that is, elements in the device are divided into a plurality of blocks and these blocks are sequentially driven in a block-by-block manner. By adopting this driving system, the number of IC driver devices can be reduced and thus the miniaturization and low cost of the device can be realized.
Referring to FIG. 1, there is shown a circuit configuration of a thermal head which employs such a divided-block drive system. More particularly, the thermal head comprises a plurality of heating elements r which are divided into four blocks A, B, C and D to be driven in a block-by-block manner, and rectifier diodes e connected directly to the associated heating elements at one end thereof, the other ends of the rectifier diodes e in each block being connected to a common electrode 1. Switching circuits Sm and Sn are provided to select one of these divided block groups. That is, when the switching circit Sm is closed at its contact a, the block A is selected, while when the circuit Sm is closed at its contact c, the block C is selected. In the same manner, when the switching circuit Sn is closed at its contact b, the block B is selected, while when the circuit Sn is closed at its contact d, the block D is selected. The heating elements r in the block A are connected at their individual electrode ends (the ends of the elements opposite to the associated rectifier diodes) to the associated heating elements r in the block C at their individual electrode ends, while the heating elements r in the block B are connected at their individual electrode ends to the associated heating elements r in the block D at their individual electrode ends, these connected points being connected by conductor wires to a plurality of associated switching circuits S, respectively. The switching circuits S function to select one of the heating elements in each block. The switching circuits S are divided into two groups, one in a first IC device 20 for driving the heating elements in the blocks A and C and the other in a second IC device 30 for driving the heating elements in the blocks B and D. The switching circuits S in the first and second IC devices 20 and 30 are both used to select one of the heating elements. For example, in driving a thermal head of the type described above, when the switching circuit Sm is closed at the contact a and the switching circuits S of the first IC device 20 are sequentially turned ON, the heating elements in the block A are sequentially selected and therefore driven. When the switching circuit Sn is closed at the contact b and the switching circuits S of the second IC device 30 are sequentially turned ON, the heating elements in the block B are sequentially driven. In the same manner, the heating elements in the blocks C and D are sequentially driven. In this way, the heating elements in one block connected at their individual ends to the individual ends of the associated heating elements in a block located one block apart from that one block to divide the heating elements into two groups and the heating elements in one of the two groups are driven by the IC device different from that of the other, whereby it can be prevented that the same IC device is driven twice continuously during switching and driving of the blocks. In particular, in the case of an image sensor, it is necessary to take into consideration the storage time necessary to accumulate an electric charge signal excited by light. For this reason, such continuous driving of the same IC device undesirably prevents the realization of high speed operation of the image sensor. Incidentally, reference numeral 10 is a power supply, and 11 is a negative resistance as shown in FIG. 1.
With the arrangement shown in FIG. 1, when 1024 of the heating elements r are connected by means of two wiring layers with a wire density of 8 wires/mm to the first and second IC devices 20 and 30 incorporating the 512-bit switching circuits S (each of the devices 20 and 30 comprising 2 128-bit IC devices), such IC wire interconnections as shown in FIG. 2 have been conventionally made. In more detail, in the prior art arrangement shown in FIG. 2, the heating elements in the blocks A and C are commonly connected at associated contact holes so as to be connected to two 128-bit IC devices 21 and 22 of the first device 20, whereas the heating elements in the blocks B and D are commonly connected at associated contact holes so as to be connected to two IC devices 31 and 32 of the second device 30. However, the prior art arrangement has been defective in that all the IC devices 21, 22, 31 and 32 must be positioned on one side of a substrate for the convenience of wiring and for the transmission of necessary signals applied to the IC devices and for connection to the power supply and furthermore, the two-layer formation of these conductor wires cannot be effectively carried out, which results in a wiring width L of the conductor wire area which becomes larger (in the case, 64 mm (=512/8)), making it difficult to make the resultant electronic device small in size and width.